Device for gasifying liquid and for metering the gas thereby obtained

ABSTRACT

Device for gasifying liquid anaesthetic, for example, and for metering the gas thereby obtained to a stream of fresh gas. The device includes a pressurized source of the liquid which is to be gasified, a gasification chamber, heating members, and a fluid-conducting member. The gasification chamber is accommodated in an elongate gasification housing whose lower part has an inlet for liquid from the source. The member for supplying the gas in a metered manner to the stream of fresh gas comprises a metering housing connected to an upper part of the gasification housing and having a metering valve. The heating members are arranged on the outside of an intermediate part of the gasification housing, in order to form a warm housing section. This housing section communicates at the bottom with the inlet, and does so via a lower heat-insulating housing section, and it is connected at the top to the upper part.

This application is the national phase of international applicationPCT/SE96/01205 filed Sep. 26, 1996 which designated the U.S.

The present invention relates to a device of the general type specifiedin the first part of claim 1.

Such a device is intended for gasifying liquid, especially liquidanaesthetic, and for metering the gas thereby obtained to a stream offresh gas, especially in an anaesthesia apparatus.

STATE OF THE ART

For a gasification chamber of the abovementioned type, the general orprinciple is that the chamber constitutes a cavity or closed space wherethe liquid in question, which is accordingly a liquid anaesthetic whenmetering gas to a fresh gas stream in an anaesthesia apparatus, isgasified and is then conveyed onwards to, and metered into, the streamof fresh gas. The basic principle of gasification is that the liquid inquestion is vaporized by being made to boil, as a result of which a 100%saturated vapour is obtained. Since the liquid which is made to boil(vaporized) and the vapour are under pressure, it can be metered ingaseous form into the stream of fresh gas by means of opening a valve inthe line via which the metering gas is introduced into the stream offresh gas. It is important in this respect that the vapour (gas) thusgenerated is cooled only after it has been metered into the stream offresh gas. Otherwise, it would be condensed, i.e. liquid would then bemetered into the stream of fresh gas as would the vapour, and this wouldlead to the vapour pressure in the fresh gas becoming unpredictable andtoo high.

For an example of a known device of the type mentioned in theintroduction, reference may be made to the metering and gasifying devicewhich is described in European Patent Specification 0 231 513. Thisknown device is intended especially for supplying anaesthetic gas to astream of fresh gas in an anaesthesia apparatus. This device comprises asource of gas at constant pressure, a second source containing a liquidwhich is to be gasified, a gasification chamber and a metering linethrough which the gas is conveyed from the chamber to a mixing pointwhere it is mixed with another gas (which is the fresh gas where theapplication involves an anaesthetic gas apparatus), and a valve devicewhich is arranged to deliver a defined dose of gas for each meteringstroke of a control valve in the valve device. The distinguishingfeature of this known metering and gasifying device is that thegasification chamber is intended to be kept at a constant pressure and,by means of a controllable heating device, to be maintained at atemperature which is such that the liquid fed from the liquid sourceinto the gasification chamber is in the main gasified directly, so thatwhen equilibrium has been reached, no more liquid is supplied from theliquid source to the gasification chamber than is dosed/metered by meansof the valve device in the metering line.

Another example of a known metering device intended for the same medicalengineering application is found in U.S. Pat. No. 5,243,973.

OBJECTS OF THE INVENTION

The primary object of the present invention is to make available adevice in which the free liquid surface inside the gasificationchamber--which is located somewhere between the lower part of thechamber (containing the liquid phase) and the upper part of the chamber(containing the gas phase)--can be maintained at a virtually constantlevel in the gasification chamber.

The underlying idea of the solution which is provided by the inventionto this problem will be that the gasification chamber is designed insuch a way that a well-defined heating zone, which can becontrolled/monitored by simple means, is obtained in an intermediatearea in the gasification housing in which the gasifi-cation chamber isaccommodated.

A secondary object of the invention will be that the gasificationhousing can be designed in a way which is simple and reliable in termsof construction and so that any variations in the level of the liquidsurface inside the gasification chamber can be easily detected, which ismade easier by the fact that the gasification housing (and with it thegasification chamber) can have a relatively elongate construction sothat the gasification chamber will have a transverse dimension which issubstantially smaller than the axial longitudinal dimension of thechamber.

DISCLOSURE OF THE INVENTION

According to the invention, the abovementioned objects are achieved byvirtue of the fact that the device specified in the introduction has thefeatures specified in the characterizing clause of Patent claim 1.

Features which represent further developments of the invention, andwhich contribute to what is from various standpoints an optimum solutionto the problem, are also to be found in dependent claims 2-8.

According to the invention, a constructional embodiment is chosen inwhich the gasification chamber is accommodated in an elongategasification housing, which has a lower part provided with an inlet forliquid from the source, and the member for supplying the gas in ametered manner to the stream of fresh gas comprises a metering housingconnected to an upper part of the gasification housing and having atleast one metering valve. The heating members are in this case arrangedon the outside of an intermediate part of the gasification housing,situated in the area between the upper part and the lower part of thegasification housing, in order to form a warm housing section whichestablishes the abovementioned well-defined temperature zone. This warmhousing section communicates at the bottom with the lower part of thegasification housing, provided with the inlet, via a lowerheat-insulating housing section, and is connected at the top to theupper part of the gasification housing via a corresponding upperheat-insulating housing section.

The gasification housing is preferably designed in such a way that theboundary wall of the gasification chamber is formed by a cylindricaljacket surface. This is achieved, for example, by the gasificationhousing being a tubular housing which is expediently arrangedessentially vertically or at least at a relatively acute angle inrelation to the vertical.

In order to make it easier to maintain a well-defined heating zone inthe warm housing section, it is expedient that the gasification housingbe made of a material with good heat conductivity, for example brass, inwhich case the intermediate part of the housing preferably has a greaterwall thickness than the two heat-insulating housing sections which areconnected to the ends of the intermediate part. The transition betweenthe intermediate part of greater wall thickness of the gasificationhousing and each adjoining heat-insulating housing section of lesserwall thickness generates a marked temperature gradient in the wallmaterial, and the lesser wall thickness of the heat-insulating housingsections means that heat conduction away from the warm housing sectionformed by the intermediate part is minimized in the heat-insulatinghousing sections.

The lower part of the gasification housing provided with the inlet (withthe inlet for the liquid from the source) is preferably designed as acold housing section which is arranged in heat-conducting communicationwith a separate cooling base. This cooling base serves to maintain theliquid surface inside the gasification chamber at an acceptable level inthe event of the internal temperature in the chamber for some reasontending to become too high.

To keep the temperature conditions as constant as possible within theintermediate part of the gasification housing, which constitutes thewarm housing section, the intermediate part is expediently provided withan effective heat insulation surrounding at least that area of theintermediate part which is provided on the outside with the heatingmembers, which expediently consist of one or more electrical heatingelements. These heating elements, which can consist of heat foils, arein this case arranged on the outside of the wall of the inter-mediatepart of the housing and surround this wall at least over a fairly largepart of its longitudinal extent.

For monitoring the temperature conditions in the warm housing section, asuitable type of temperature sensor, for example a thermistor, isarranged preferably in the area of the lower end of the intermediatepart of the housing, on the inside of the housing wall. The outputsignal from this temperature sensor can then be used for controlling thepower of the electrical heating members. Similarly, a temperature sensormay expediently be arranged on the inside of the housing wall in thearea of the upper end of the intermediate part of the housing. Theoutput signal from this temperature sensor can be used in an alarmfunction for temporarily interrupting the supply of gas to the stream offresh gas or for interrupting the gasification of liquid in thegasification chamber by interrupting the current supply to theelectrical heating members which surround the intermediate part of thegasification housing.

The metering housing mounted on the upper part of the gasificationhousing preferably comprises a valve plate provided with a separateelectrical heating element, and, connected to this valve plate, ahousing part which conveys the fresh gas and which has a continuouspassage for the fresh gas. One end off this gas passage constitutes theinlet for the stream of fresh gas, while the other end of the passageconstitutes the outlet for the fresh gas which, via a channel adjoiningthe gas passage inside the housing part, has been enriched with gasgenerated in the gasification chamber. For effecting this supply of gasto the stream of fresh gas, the gas passage through the housing part isin communication with the gasification chamber via channels in themetering valve, the valve plate, and the housing part connected thereto.

The valve plate, which can be designed, for example, as a rectilinearplate or an otherwise designed construction, not only bears the meteringvalve, which can be a solenoid valve for example, but also a backflowvalve. The purpose of this backflow valve is to use separate backflowgas, for example oxygen or air, to force non-gasified liquid back fromthe gasification chamber to the liquid source after the gasification inthe gasification chamber has ended. Such a backflow is needed, forexample, when replacing the liquid which is to be gasified in thegasification chamber. The backflow valve then communicates, on the onehand, with a backflow gas source via a channel in the valve plate, and,on the other hand, communicates with the gasification chamber viachannels in the valve plate.

The metering valve is expediently arranged axially in line with thegasification housing on the side of the valve plate directed away fromthe housing, while the backflow valve is expediently arranged on thesame side of the valve plate as the gasification housing. With thegasification housing arranged vertically, the metering valve is thendirected straight up from the top side of the valve plate, while thebackflow valve is directed straight down from the underside of the valveplate, parallel to the preferable tubular gasification housing.

BRIEF DESCRIPTION OF THE FIGURES IN THE DRAWING

The invention will now be described and explained in greater detailbelow, with reference to the attached drawings which show an embodimentof the device according to the invention. In the drawings:

FIG. 1 shows major parts and members of a device according to theinvention, seen in perspective;

FIG. 2 shows a longitudinal section through the device shown in FIG. 1and FIG. 3, along the line of sectioning II--II in FIG. 3;

FIG. 3 shows a side view of the device in accordance with FIG. 2, asseen in the direction indicated by the arrow S in FIG. 2;

FIG. 4 shows a longitudinal section through the lower half of thegasification housing of a device according to the invention, shown in avery schematic representation as background to the temperature curves inFIG. 5;

FIG. 5, finally, shows the ideal temperature profile and a morerealistic temperature profile for the fluid (the liquid/gas (vapour))inside the part, shown in FIG. 4, of the gasification chamber in thegasification housing of the device.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a perspective representation of major parts and members ofa device according to the invention intended for gasifying liquid. Inthis particular case, the device is intended for gasifying liquidanaesthetic, and for metering the anaesthetic gas thereby obtained to astream of fresh gas for an anaesthesia apparatus (not shown). Connectedto the device in this case is a liquid source 2, not shown in FIG. 1,but indicated in FIG. 2, which liquid source is under preferablyconstant pressure and contains the liquid anaesthetic which is to begasified in the device.

The device shown in FIGS. 1-3 comprises a tubular gasification housing 4with a lower part 6 provided with an inlet 8 for the liquid anaestheticsupplied from the source 2 through a line 10. This liquid anaestheticflows in from the inlet 8 via a pair of channels 12 and 14 at the lowerend of a cylindrical gasification chamber 16 accommodated in thegasification housing 4. At the upper end of the gasification chamber 16there is a fluid-conducting member 20 which is provided with a meteringvalve 18 and is used for supplying gas in a metered manner from thechamber 16 to the stream of fresh gas for the abovementioned anaesthesiaapparatus (not shown here). The gasification housing 4 has an upper endpart 22 which is connected tightly to a downwardly directed tube section24 on the underside of the fluid-conducting member 20.

As can be seen from FIGS. 2 and 3, the member 20 comprises a meteringhousing 25 which is connected to the upper part 22 of the gasificationhousing and which in turn comprises a parallelepipedal valve plate 26and, connected to the latter, a housing part 28 which conveys fresh gasand has a continuous gas passage 30 for the stream of fresh gas which isadded, inside the housing part 28, to the gas from the gasificationchamber 16. The housing part 28 can constitute an integrated part of thevalve plate 26. The flow path of the gas from the gasification chamber16 to the passage 30 for fresh gas will be described hereinbelow.

As can be seen from FIGS. 1-3, the gasification housing 4 is provided onthe outside with heating members 32. These heating members expedientlyconsist of one or more electrical heating elements, preferably of theheat foil type.

As can be seen in particular from FIG. 2, the heating members 32 arearranged on the outside of an intermediate part 34 of the gasificationhousing which is located between the upper part 22 of the gasificationhousing 4 and the lower part 6, and which has a comparatively thickwall. This intermediate part 34, which constitutes the warm housingsection of the device, communicates at the bottom with the lower part 6of the gasification housing, provided with an inlet, and does so via alower heat-insulating housing section 36 which has a comparatively thinwall. Similarly, the intermediate part 34 communicates at the top withthe upper part 22 of the gasification housing 4 via an upperheat-insulating housing section 38 which has a comparatively thin wall.

The gasification housing 4, which is a tubular housing in the embodimentshown, is made of a material with good heat conductivity, such as brass,for example. As can be seen from FIG. 2, the intermediate part 34 of theclassification housing 4, and also the upper part 22 and lower part 6 ofthe housing, have a considerably greater wall thickness than the twoheat-insulating housing sections 36 and 38. These two thin-walled,heat-insulating housing sections in this way function as temperatureinsulators in the axial direction of the gasification housing. The lowerpart 6 of the gasification housing, provided with the inlet, forms thecold housing section of the device, which cold section is expediently indirect heat-conducting communication with a cooling base 40 which isonly schematically indicated and whose temperature is designated T₄₀ inFIG. 5.

The heating members 32 surrounding the intermediate part 34 of thegasification housing surround the said intermediate part of the housingover at least a fairly large part of its longitudinal extent. In orderto maintain the desired temperature conditions and temperature gradientsin that part of the gasification chamber 16 located in the intermediatepart 34, an outer, sleeve-like heat insulator 42 is arranged around thegasification housing 4, at least over that part of the housing where theheating members 32 are present.

In the area of the lower end of the intermediate part 34 of the housing,a temperature sensor 44, for example a thermistor, is arranged on theinner side of the housing wall, the output signal from this temperaturesensor 44 serving to control the power of the electrical heating members32. In the area of the upper end of the intermediate part 34 of thehousing, and again on the inner side of the housing wall, there is afurther temperature sensor 46 whose output signal is used in an alarmfunction, for example for temporarily interrupting the metered supply ofgas to the stream of fresh gas or for interrupting the gasification ofliquid in the gasification chamber 16. FIG. 2 shows diagrammatically acontrol means 48 acted on by the temperature sensors 44 and 46 and usedfor controlling the current supply to the heating members 32.

We now pass to a more detailed examination of the fluid-conductingmember 20 located at the upper end of the gasification housing 4, withreference being made in particular to FIG. 2 and FIG. 3.

The fluid-conducting member 20, which thus manages the supply of gasfrom the chamber 16 to the stream of fresh gas in the passage 30,consists of a metering housing which comprises the valve slate 26provided with a separate electrical heating element 50, and the housingpart 28 connected to the rear side of the valve plate and having thecontinuous gas passage 30. The fresh gas flowing to the anaesthesiaapparatus (not shown here) enters the gas passage 30 at the inlet endthereof and then, after having been enriched with metered fresh gasinside the housing part 28, flows out from the passage 30 via the outletend thereof.

In addition to the metering valve 18, which can be a solenoid valve forexample, the valve plate 26 also has a backflow valve 52. This backflowvalve serves, with the aid of backflow gas, for example oxygen or air,to force residual non-gasified liquid back from the gasification chamber16 to the liquid source 2 after gasification in the gasification chamberhas ended. This situation arises, for example, when replacing the liquidwhich is to be gasified in the gasification chamber 16. The backflowvalve 52, which is mounted in a bore 54 in the valve plate 26,communicates at the top with a backflow gas source 60 via a line 56 andan inlet 58. Inside the backflow valve 52 there are a pair of axialchannels 60 and 62 and a radial channel 64 adjoining the upper end ofthe channel 62. When the movable valve element 66 of the valve issituated in a lower position, gas can flow from the inlet 58 via thechannels 60, 62 and 64 to the horizontal channel 68 in the valve plate26. The channel 68 opens into a bore 70 in the valve plate 26, whichbore 70 is in direct and open communication with the upper end of thegasification chamber 16. When the gasified anaesthetic is to be meteredinto the fresh gas which is flowing through the passage 30, the backflowvalve 52 is of course closed, i.e. the valve element 66 is then situatedin an upper closure position which prevents mutual communication betweenthe channels 60 and 62 in the backflow valve 52.

The metering valve 18, for its part, contains the two axial channels 72and 74 and also the transverse channel 76 issuing radially from thelower end of the channel 74. The channels 72 and 74 communicate witheach other when the movable valve element 78 of the metering valve 18 issituated in a raised opening position. By contrast, when the valveelement 78 has been switched by magnetic actuation to a lower closureposition, fluid cannot flow between the channels 72 and 74. The radialchannel 76 opens out into a circular track 80 on the outside of theattachment part 82 of the metering valve 18 held in the valve plate 26.As can be seen from FIG. 3, the circular track 80 communicates with thefresh gas passage 30 via a radial channel 84 in the valve plate 26 and achannel 86 in the housing part 28 coaxially adjoining the channel 84.The channel 86 opens into the fresh gas passage 30 and the supply of gasfrom the gasification chamber 16 to the fresh gas in the passage 30 thustakes place at the point where the channel 86 opens into the passage 30.

During ongoing gasification in the gasification chamber 16, the backflowvalve 52 is closed, and the gas from the chamber 16 can then flow fromthe bore 70 via the channels 72, 74 and 76 and the circular track 80 andthe coaxial channels 84 and 86 to the fresh gas passage 30 where themixing takes place.

The control of the gasification in the chamber 16 will now be describedin brief with reference to the diagrammatic FIGS. 4 and 5 which describethe function and in which those parts directly corresponding to theembodiment according to FIGS. 1-3 have been given the same designationsas in these three figures.

The lower part of the gasification chamber 16 will at all times containthe liquid phase of the supplied liquid anaesthetic, while the upperpart of the gasification chamber 16 will contain the gas phase of theanaesthetic. Somewhere between these there will be a liquid surface G.In compliance with the primary objective of the invention, the level ofthis surface will be maintained as constant as possible. To achievethis, the temperature of the walls of the gasification chamber must becontrolled and monitored carefully. The lowermost part of thegasification chamber will be maintained at a temperature which liesbelow the boiling point of the anaesthetic, and that part of thegasification chamber situated above the lowermost part will bemaintained at a temperature in excess of the boiling point. Betweenthese two temperature zones there is a gasification housing section 36with comparatively thin walls, which section functions as a temperatureinsulator. The temperature profile there is not known in detail, but ithas to be a continuous function of the height and must increaseconstantly. The thick walls of the upper housing sections have a highheat conductivity (brass is a good conductor of heat) which keeps thetemperature virtually constant in the vertical direction. The idealtemperature profile is designated T_(i) and is shown by a dashed line inFIG. 5. At the lower end of the warm housing section (to the inside ofthe heating members 32) there is a temperature sensor 44 which is usedfor temperature control, i.e. this is the location which the controlmeans attempts to maintain at the set temperature T_(r) for the warmsection. At the upper end of the warm housing section there is atemperature sensor 46 whose detected temperature will at all times lieabove the boiling point. Should this temperature drop below the boilingpoint (T_(kp)), then the level of the liquid surface is probably toohigh up in the gasification housing 4. If this happens immediately aftera large, gradual increase in the metering, then it should be possible tostop the metering for a short time in order to give the heating members32 the possibility of "catching up". If, on the other hand, this happensduring normal metering, then it is a matter of a serious error, and analarm signal must then be generated and the gasification interrupted.

In practice, the temperature profile will not of course be as favourableas in the ideal case which is represented in FIG. 5 by the dashed lineT_(i). In practice, the temperature will not be constant in the verticaldirection in the sections without heat insulating. In the horizontaldirection, the anaesthetic will not have the same temperature as thewalls. A somewhat more realistic temperature profile is shown by thedot-and-dash line in FIG. 5 and is designated T_(v). The phase boundarybetween the liquid phase and gas phase of the anaesthetic is designatedG_(i) in FIG. 4 for the ideal case and G_(v) for the more realistic"actual" case.

We claim:
 1. Device adapted to gasify a liquid and arranged for meteringthe gas thereby obtained to a stream of fresh gas, the device comprisinga source (2) of a liquid which is to be gasified, a gasification chamber(16) communicating with the liquid source and having heating members(32), and a fluid-conducting member (20) provided with a metering valve(18) and adapted to supply gas in a metered manner from the chamber (16)to the stream of fresh gas, characterized in that the gasificationchamber (16) is accommodated in an elongate gasification housing (4),having a lower part (6) provided with a liquid inlet (8) for supplyingliquid from the source, fluid-conducting member (20) comprises ametering housing connected to an upper part (22) of the gasificationhousing (4) and having at least one metering valve (18), that theheating members (32) are arranged on the outside of an intermediate part(34) of the gasification housing, situated between the upper and lowerparts (22 and 5) of the gasification housing (4), in order to define awarm housing section, that the warm housing section,which is providedwith said heating members (32), communicates at the bottom with thelower housing part (6) with the inlet (8), and does so via a lowerheat-insulating housing section (36), that the warm section is connectedat the top to the upper housing part (22) via an upper heat-insulatinghousing section (38),and that temperature sensors (44,46) are arrangedin the intermediate housing part (34) and connected to act on a controlmeans (48) controlling the power supply to the heating members (32). 2.Device according to claim 1, characterized in that the gasificationhousing is a tubular housing (4) made of a material with, good heatconductivity, for example brass, and the intermidiate part (34) of thehousing, and its upper and lower parts (22 and 6, respectively), have agreater wall thickness than the two heat-insulating housing sections(36, 38), and in that the lower part (6) of the gasification housingprovided with the inlet forms a cold housing section which is arrangedin heat-conducting communication with a cooling base (40).
 3. Deviceaccording to claim 1, characterized in that the heating members consistof at least one electrical heating element (32), such as a heating foil,which is arranged on the outside of the wall of the intermediate part(34) of the housing and surrounds this wall at least over a fairly largepart of its longitudinal extent.
 4. Device according to claim 3,characterized in that a temperature sensor (44) is arranged in the areaof the lower end of the intermediate part (34) of the housing, on theinside of the housing wall, the output signal from this temperaturesensor (44) serving to control the power of the electrical heatingmembers (32), and in that a temperature sensor (46) is arranged on theinside of the housing wall in the area of the upper end of theintermediate part of the housing, the output signal from thistemperature sensor (46) being used in an alarm function for temporarilyinterrupting the supply of gas to the stream of fresh gas or forinterrupting the gasification of liquid in the gasification chamber(16).
 5. Device according to claim 1, characterized in that the meteringhousing, which is mounted on the upper part of the gasification housing,comprises a valve plate (26) provided with a separate electrical heatingelement (50), and, connected to this valve plate, a housing part (28)which conveys the fresh gas and which has a continuous gas passage (30)whose one end constitutes the inlet for the stream of fresh gas andwhose other end constitutes the outlet for the fresh gas which has beenenriched with metered gas, and which gas passage (30) communicates withthe gasification chamber (16) via channels (70, 72, 74, 76, 80, 84, 86)in the metering valve (18), the valve plate (26), and the housing part(28) connected thereto.
 6. Device according to claim 5, characterized inthat the valve plate (26) not only bears the metering valve (18), whichis preferably a solenoid valve, but also a backflow valve (52) whichuses separate backflow gas, for example oxygen, to force non-gasifiedliquid back from the gasification chamber to the liquid source (2) afterthe gasification in the gasification chamber (16) has ended, for examplewhen replacing the liquid which is to be gasified, and the backflowvalve (52) communicates, on the one hand, with backflow gas source (60)via a channel (58) in the valve plate (26), and, or the other hand,communicates with the gasification chamber (16) via channels (68, 70) itthe valve plate (26).
 7. Device according to claim 6, characterized inthat the metering valve (18) is arranged axially in line with thegasification housing (4) on the side of the valve plate (26) directedaway from the housing, while the backflow valve (52) is arranged on thesame side of the valve plate as the gasification housing.
 8. Deviceaccording to claim 1, characterized in that the intermediate part (34)of the gasification hosing (4) is provided with a heat insulation means(42) surrounding at least that portion of the intermediate part- whichbears the heating members (32).